The objectives of this research project are to develop a radioactively-labelled marker for sodium channels in excitable membranes and to use that marker to study the structure of such channels and their spatial distribution in a variety of nerves and muscles tissues. This year we are studying the competition between drugs, ions, and the marker, a highly tritiated neurotoxin called saxitoxin (STX). We are also studying the binding of saxitoxin to cardiac membranes and to normal and denervated skeletal muscle. We are probing the spatial distribution using autoradiographic methods, and we are studying the binding to non-nervous cells which occur normally in nervous tissues, i.e., glia.